Method of underground storage in a reservoir



y 1968 w. H. VAN EEK 3,385,067

METHOD OF UNDERGROUND STORAGE IN A RESERVOIR Filed March 8, 1966 FIG. 2 INVENTORI WOUTER H. VAN EEK W/OWW HIS ATTORNEY United States Patent 3,385,067 METHOD OF UNDERGROUND STORAGE IN A RESERVOIR Wouter H. van Eek, The Hague, Netherlands, assignor to Shell Oil Company, New York, N.Y., a corporation of Delaware Filed Mar. 8, 1966, Ser. No. 532,789

Claims priority, application Netherlands, Mar. 10, 1965,

3 Claims. (51. 61-5) ABSTRACT OF THE DISCLOSURE A method for storing a liquid product in an underground storage reservoir comprising two cavities interconnected below their highest parts by a conduit. The conduit is filled with a displacing fluid heavier than and immiscible with the liquid conduct. The cavities are partially filled with the displacing fluid and the remaining volume of one cavity is charged with pressurized gas while the remaining volume of the other cavity is filled with liquid product. In this manner, fluid may be flowed and displaced selectively from one cavity to another solely under the combined pressure of the pressurized gas.

This invention relates to the method and apparatus for storing a liquid product, in particular, hydrocarbons, such as for example, crude petroleum.

In the production of petroleum it is often necessary to store the produced oil temporarily in the vicinity of the oil Wells. This storing of the produced oil presents a problem, particularly when the oil wells are situated in the sea.

Although underground storage of petroleum products has been used in the industry, many difficulties in the subsequent extraction of such stored products heretofore remain. Specifically, the underground cavities required for such storage are frequently quite deep and the pumping costs are consequently quite high. If the pump is in the bottom of the cavity, maintenance is difficult if not impossible. Furthermore, if the underground storage cavity is beneath the sea or other large body of water it is equally difiicult, if not impossible, to provide power to the pump for operation since the construction of permanent platforms for a requisite prime mover under such conditions is impractical if not prohibitively expensive.

An object of this invention, therefore, is to solve these problems in a simple and relatively inexpensive manner.

To this end, the liquid product of an oil well, according to the invention, is forced into an underground storage reservoir filled with a displacing liquid which is heavier than and immiscible with the liquid product. The said displacing liquid is thereby displaced at least partially from the storage reservoir via a conduit into a second underground reservoir situated at a level equal to or higher than the level of the storage reservoir. A gas under pressure is present in the second reservoir above said displacing liquid.

A suitable displacing liquid is, for example, a salt solution, although other displacing liquids may be used. The essential criteria, however, are that the displacing liquid must be heavier than and immiscible with the liquid product.

The liquid product is, for example, crude petroleum, but it will be obvious that, if desired, other liquid such as gas oil, liquefied butane or propane can also be stored by means of this method.

The gas under pressure employed can be, for example, methane, propane, butane, mixtures thereof or any other suitable gas.

3,385,067 Patented May 28, 1968 "ice The storage installation for use with this method comprises, according to the invention, a first underground storage reservoir provided with a supply and discharge line for the liquid product, a second underground reservoir situated at a level equal to or higher than the level of the first reservoir, a connecting line which connects the lower part of the first reservoir with the lower part of the second reservoir, a displacing liquid in the first reservoir, a supply and discharge line for the displacing liquid connected to the second reservoir and a line for the supply of gas under pressure to the second reservoir.

The said reservoirs can be advantageously arranged in an underground salt bed. When the invention is used in the production of oil from wells situated in the sea, the said reservoirs can be situated below the bottom of the sea, for example, in a salt bed lying beneath the sea bottom.

The invention will now be described with reference to the accompanying drawing wherein:

FIGURE 1 shows a cross-section of the earth prepared for one embodiment of the invention and FIGURE 2 shows a cross-section of the earth prepared for another embodiment of the invention.

In both figures of the drawing like reference characters denote like structure.

With reference to FIGURE 1, the surface of the sea or other body of water is designated by numeral 1, and the bottom of the sea by numeral 2. Beneath earth formations 3 below the sea bottom 2 are, for example, other layers of a different material such as rock 5. In the salt beds 4 a storage reservoir 6 is arranged, the lower part of which is connected to the lower part of a second reservoir 7 by means of a connecting line 20. The reservoirs 6 and 7 can be formed in a salt bed by locally dissolving the salt with water, for example, sea water, and removing the salt in a dissolved state.

The storage reservoir 6 is provided with a supply line 10 and a discharge line 11, both for the liquid product. In place of the two lines 10 and 11, a single line may be used which serves both as supply and discharge line for the liquid product. It is also possible to design lines 10 and 11 concentrically. Valves 14 and 15 are arranged in lines 10 and 11. The second reservoir 7 is provided with a supply and discharge line 12 having a valve 16 for the displacing liquid. A line 13, provided with a valve 17, is likewise connected to the second reservoir 7. The line 13 serves to supply gas to the reservoir 7. As with lines 10 and 11, lines 12 and 13 may also be concentrically arranged.

The only difference between the storage installation according to FIGURE 1 and that according to FIGURE 2 is that according to the former the reservoir 7 is situated at a higher level than storage reservoir 6, while in the latter installation both reservoirs 6 and 7 are situated at the same level.

The operation of the storage reservoir described above is as follows:

Let it be assumed that the installation is completely filled with the displacing liquid, for example, a salt solution. With valves 14 and 17 closed, and valves 15 and 16 open, liquid product, for example, petroleum, is now pumped through a line 10 into a storage reservoir 6. The liquid product thus displaces the salt solution and the latter flows out through line 12. The supply of petroleum is continued until storage reservoir 6 is completely filled therewith. Valve 15 is subsequently closed and valve 17 opened. This means that valves 16 and 17 are in the open position. Gas under pressure, for example, under a pressure of twenty atmospheres, is now supplied to reservoir 7 via line 13. This supply of gas under pressure will again cause salt solution to flow away via line 12. The supply of gas under pressure via line 13 is continued until sufiicient salt solution has flowed away via line 12 and until a sufiiciently large cushion of gas has formed above the salt solution 9 in reservoir 7. The valves 16 and 17 are then closed. The situation is then as shown in the figures.

The separating surface between the salt solution 9 and the petroleum 8 has at this point, for example, reached the level designated by 21 and 22 in FIGURES 1 and 2, respectively. The salt solution has reached the level 23 and 24 (in FIGURES 1 and 2, respectively). If it is desired to withdraw oil from the storage installation, valve 14 is opened. Due to the hydrostatic pressure of the salt solution and the gas pressure (FIGURE 1) or due to the gas pressure alone (FIGURE 2), salt solution 9 is now forced from reservoir 7 via connecting line 20 into the storage reservoir 6. As a result, petroleum flows out through line 11 and valve 14. When a sufiicient amount of petroleum 8 has been withdrawn, valve 14 is closed again.

Whenever petroleum has to be stored again, it is pumped via line 10 into reservoir 6, valve 14 being closed and valve 15 open. As a result, an amount of salt solution 9 is displaced into reservoir 7 from reservoir 6. Consequently, the pressure of the gas above the level 23 or 24 of the salt solution 9 in reservoir 7 increases gradually. The accumulated pressure can be used again in a later Withdrawal of a quantity of petroleum from the storage installation.

I claim as my invention:

1. A method for storing a liquid product in an underground storage reservoir comprising two cavities interconnected below the highest parts thereof by a conduit including the steps of:

filling said interconnecting conduit with a displacing fluid that is heavier than and immiscible with said liquid product;

partially filling said cavities with said displacing fluid;

charging the remaining volume of one cavity with pressurized gas;

filling the remaining volume of the other cavity with said liquid product; and

flowing and displacing fluid selectively from one of said cavities to the other solely under the combined pressure of said pressurized gas.

2. A method as described by claim 1 wherein said one cavity is disposed at a higher elevation than said other cavity.

3. A method as described by claim 1 wherein said one cavity is disposed at substantially the same elevation as said other cavity.

References Cited UNITED STATES PATENTS 2,934,904 5/1960 Hendrix 61.5 2,947,147 8/1960 Johnson 61-.5 2,961,841 11/1960 Giles 61.5 X 3,003,322 10/1961 Jordan 61--.5 3,253,414 5/1966 Molique 61-.5

EARL I. WITMER, Primary Examiner. 

